HISTORY OF GLACIATIONS IN THE NEPAL HIMALAYAS AND RECONSTRUCTION OF PALAEOCLIMATE SINCE THE LAST GLACIAL

The aerial photo interpretation and field observations clarified morphostratigraphy of glacial moraines and it led to the classification of the glacial advances into at least five stages throughout the Nepal Himalayas. The stage classification could be confirmed by relative dating values mainly based on weathering criteria. Optically stimulated luminescence and carbon dating were used to elucidate the timing of past glacial stages. The resulting ages suggest that glaciers expanded at the Little Ice Age, the Holocene, the Late Glacial, and the late and early substages of the Last Glacial. The two substages could be correlated with the global Last Glacial Maximum (LGM) and Marine Isotope Stage 3. Timing of glacial stages looks synchronized glaciation throughout the Nepal Himalayas. Valley glaciers had extended nearly to the same termini from the Late Glaciation to the LIA. Even in the LGM and MIS 3, the termini were enlarged somewhat larger than those of the Late Glacial. This fact suggests that the glaciation was restricted even during the Last Glacial. Summer monsoon precipitation plays an essential role in glacier accumulation of the Nepal Himalayas. However, summer monsoon is relatively more intensified toward the east, and glaciers are maintained by both monsoon and winter westerly precipitation rainfall in the west. Enhanced southward inclination of glacial equilibrium-line during the LGM suggests weakened monsoon restricted glacial advance but the lower air temperature feebly encouraged glacial extension. Moreover, winter westerlies, shifted father to the south, did not flow over the Himalayas. And, less winter precipitation controlled glaciers to advance modestly. In this way, relative climatic enhancement between monsoon and westerlies controlled the style and timing of glaciations in the Himalayas.